Table of Contents
CloudWatch Alarms are the silent watchdogs of your AWS environment, always ready to act when things go wrong. Arjun, like many AWS beginners, once wondered: “Okay, CloudWatch collects metrics… but how do I actually respond when an issue happens?” That’s when he discovered the power of CloudWatch Alarms — the feature that not only monitors thresholds but also takes action to keep your cloud safe and reliable.
🎯 What Are CloudWatch Alarms?
CloudWatch Alarms monitor metrics and take action when thresholds are crossed.
Think of it like this:
“If CPU usage is over 80% for 5 minutes, alert me!”
“If disk space drops below 10%, reboot the instance!”
Simple rules, powerful outcomes.
🚦 Alarms Have 3 States
| State | Meaning |
✅ OK | All is well. |
⏳ INSUFFICIENT_DATA | Not enough data to decide. |
🔴 ALARM | Threshold crossed. Take action! |
⏱️ The Heartbeat: Period
Period = how often you check the metric.
- Can be as short as 10 seconds (high-resolution metric)
- Or as long as 5 minutes, depending on what you need
Arjun set his alarm to check CPU every 60 seconds. That was enough for his use case.
🛠️ What Can an Alarm Do?
An alarm isn’t just about shouting.
It can actually do things:
- Take action on EC2 instances
- Stop, terminate, reboot, recover
- Trigger Auto Scaling
- Add/remove EC2s based on load
- Send notifications
- 🔔 Push to SNS topic
- 📩 Notify email/SMS
- 🤖 Call Lambda for custom logic
When Arjun’s app went down once due to a full disk, he set up an alarm that automatically notified him AND triggered a Lambda to clean up logs. Crisis avoided.
🤹♂️ Composite Alarms — The Smart Combo
Arjun noticed a problem: too many alarms were firing. He needed to get smart.
So he used Composite Alarms.
Here’s how they work:
- Combine multiple alarms using
AND/ORlogic. - Get notified only when multiple conditions are true.
Example:
✅ CPU > 80% AND Disk I/O high → Trigger alert
❌ CPU > 80% but Disk I/O normal → Ignore it
This helped Arjun reduce alarm noise and focus only on real issues.
🛡️ EC2 Instance Recovery with Alarms
Arjun wanted peace of mind in case EC2 failed. So he used CloudWatch Alarms to trigger EC2 recovery based on status checks:
| Check Type | What It Monitors |
| Instance Status | EC2 OS health (like kernel panic) |
| System Status | Host hardware issues |
| EBS Status | Attached disk health |
If the host failed, the alarm automatically moved his instance to a healthy host.
Same IP. Same data. No stress.
🧠 Bonus: Log-Based Alarms
Arjun was monitoring an app log file for the word ERROR. He created a CloudWatch Log Metric Filter, and tied that to an alarm.
Now if ERROR appears more than 10 times in 5 minutes, he gets an alert.
Simple setup. High confidence.
🧪 Test Before You Trust
Before going live, Arjun tested everything using this CLI command:CopyCopy
aws cloudwatch set-alarm-state \
--alarm-name "CPUHigh" \
--state-value ALARM \
--state-reason "Testing alarm action"
This simulated a breach and confirmed SNS and Lambda triggers were working.
📌 SAA-Certified Knowledge
If you’re prepping for the AWS SAA exam, remember:
✅ CloudWatch Alarms monitor metrics
✅ Can trigger EC2 actions, SNS, Auto Scaling
✅ Composite Alarms = Combine logic across alarms
✅ Can be tied to Log Metric Filters
✅ Support EC2 recovery actions
✅ Use IAM roles properly when needed
✅ CLI command: set-alarm-state for testing
🧘 Arjun’s Takeaway
“CloudWatch collects data.
Alarms give it a voice.”
He now sleeps peacefully, knowing CloudWatch is watching over his infrastructure — and will shout (or act) if anything goes wrong.
FAQ
Q1: What are CloudWatch Alarms in AWS?
CloudWatch Alarms let you monitor metrics and trigger actions such as notifications, EC2 recovery, or Auto Scaling when thresholds are breached.
Q2: What are the three states of a CloudWatch Alarm?
A CloudWatch Alarm can be in one of three states: OK, INSUFFICIENT_DATA, or ALARM, depending on the metric’s threshold evaluation.
Q3: Can CloudWatch Alarms automatically recover EC2 instances?
Yes. CloudWatch Alarms can trigger EC2 recovery actions when instance or system status checks fail, ensuring uptime with minimal manual effort.
Q4: What is a Composite Alarm in CloudWatch?
A Composite Alarm combines multiple CloudWatch Alarms with AND/OR logic, helping reduce noise by alerting only when multiple conditions are true.
Q5: Can CloudWatch Alarms be tied to CloudWatch Logs?
Yes. You can create a Log Metric Filter and connect it to a CloudWatch Alarm to trigger alerts when log events (like “ERROR”) appear frequently.
Read More on AWS Monitoring
- Amazon CloudWatch Logs Insights: A Beginner’s Guide
- Difference between AWS CloudWatch, CloudTrail and Config
- Understanding AWS EventBridge: The Automation Service Explained
- Understanding AWS CloudWatch Alarms: Listen to Your Cloud Signals
- How CloudWatch Agent Completes EC2 Monitoring: A Comprehensive Guide
- Understanding Live Tail in Amazon CloudWatch Logs
- Master AWS Resource Monitoring with CloudWatch Metrics
- An Introduction to CloudWatch Logs: What You Need to Know
- Understanding Amazon CloudWatch: A Comprehensive Guide
